In cellular telephones and other communication devices, radio frequency (RF) power amplifiers are typically used to amplify RF signals prior to transmission. These RF power amplifiers typically generate an output power in the range of 50 mW to 3 watts. In such devices, linear amplification is desired to prevent signal distortion. Efficiency is also a consideration, especially for mobile devices such as cellular telephones, due to the limited quantity of energy stored in the accompanying battery.
Efficiency and linearity are often competing considerations. When high efficiency is important, a low amplifier transistor bias current is chosen, thereby increasing battery life and talk time. This generally results in acceptable distortion at low to moderate power levels, but creates unacceptable distortion at high power levels. When high linearity is important, a larger transistor bias current is chosen, reducing distortion to an acceptable level even at high power levels. The high bias current may also be required to obtain the maximum output power from the amplifier output transistor. However, the high bias current reduces battery life and talk time, particularly at low power levels.